MXene Lubricated Tribovoltaic Nanogenerator with High Current Output and Long Lifetime

Highlights Successfully solves the key issue of tribovoltaic nanogenerators (TVNGs) lifetime (90,000 cycles) and improves its output current density (754 mA m−2) simultaneously. Conductive polar liquid with MXene as additive is proposed as the dominant factor in enhancing the electrical output performance and durability of TVNG simultaneously. The mechanism of lubricated TVNG with enhanced output performance is explained from the perspective of solution polarity at the first time. Mxene solution exhibits universality in different types of semiconductor systems (Cu and P-type Si, and Cu and N-GaAs as material pairs). Supplementary Information The online version contains supplementary material available at 10.1007/s40820-023-01198-z.


Note S1 The polar liquid interface lubrication strategy mention in this manuscript has the same effectiveness in rotating TVNG
Compared with linear motion, rotational motion is more convenient to operate, hence, we also explore the performance of rotary TVNGs with interface lubricants.The 3D structure diagram of rotary TVNG is shown in Fig. S11a, where mainly consists of a rotor and a stator, and different liquids were added to the interface as lubricants.Simplify, the rotor of TVNG is mainly consists of Cu electrode (Fig. S11a(i)), and the stator is composed of P-type Si (Fig. S11a(i)).Figure S11b-e show the short-circuit current output and open-circuit voltage output of TVNGs without interface lubricant (TVNG), paraffin oil lubricated TVNG (oil-TVNG), DI lubricated TVNG (DI-TVNG), and MXene solution lubricated TVNG (MXene-TVNG), respectively.It can be seen that the short-circuit currents of all four TVNGs increase with the increase of rotate speed, but open-circuit voltages have a litter change.When the rotate speed is 3 r s -1 , the short circuit currents of TVNG without interface lubricant, oil-TVNG, DI-TVNG, and 4.667,189.17,and 434.65 μA, respectively.Apparently, MXene-TVNG has a better output performance compared with the other interface lubricated rotary TVNGs.Fig. S11f and Fig. S11g show the peak current and peak power density (PPD) of MXene-TVNG at different rotation speeds along with the external loads.Clearly, greater values of peak current and PPD can be obtained at larger rotation speed.Specifically, MXene-TVNG has low-impedances of 1, 1, and 3 kΩ at 3, 2 and 1 r s -1 , where the corresponding peak currents are 160.498,125.24,and 39.12 μA and maximum PPDs are 23.54,14.33,and 4.19 mW m -2 , respectively.After 26,500 cycles, the MXene-TVNG still maintains 91% current output compared with initial value of 80.44 μA (Fig. S11h).However, the TVNG still maintains 32.2% current output compared with initial value of 13.18 μA after 2,000 cycles.Hence, MXene Nano-Micro Letters S10/S10 solution as an interface lubricant for rotating TVNG still has the effect of improving the current output and lifetime simultaneously.In addition, the lifetime of rotating TVNG is not as long as that of linear TVNG.The possible reason is that with the addition of 3 ml MXene solution, the interface contact area of rotating TVNG (diameter 3.8 cm) is larger and the consumption of interface lubricant is faster.To sum up, polar liquid interface lubrication strategy mention in this manuscript has the same effectiveness in rotating TVNG.

Note S2 The effect of dispersity on lubricity of MXene solution, the ways to avoid MXene agglomeration
Good dispersion can prolong the effectiveness of MXene solution.If the MXene solution is agglomerated, the lubricity will be weakened and the lifetime of TVNG will be reduced.In this work, to avoid the precipitate of MXene, we stir the solution to make it evenly disperse in the water before measuring the output performance of TVNG.In addition, during the sliding process, the MXene solution will have molecular motion along with the slider movement, which is also beneficial for the uniform dispersion of MXene solution.

Fig
Fig. S2 I-V curve of TVNG (P-type Si and Cu) at different pressures (without adding lubricant at the interface)

Fig. S15
Fig. S15 AFM image of the N-type GaAs

Fig. S18
Fig. S18 3D optical surface profiler images of N-type GaAs without lubricant i after 90,000 stability tests, and the 3D optical surface profiler images of MXene-TVNG ii after 90,000 stability tests